Duplex telegraph system



Aug. 19, 1930r J, w, MlLNOR ET AL 1,773,371

DUPLEX TELEGRAPH SYSTEM Filed 001;. 30, 1928 HR l ClRL \JNE Fig.1?

AL LC gwventow W. M \LNOR D. C AN NON Patentecl Aug. 19, 1930 r UNITED STATES PATENT OFFICE JOSEZ PH W. MILNOR, OF. MAPLEWOOD, AND WILLIAM D. CANNON, OE METUCHEN, NEW

. JERSEY, ASSIGNORS TO THE WESTERN UNION TELEGRAPH COMPANY,OF NEW YORK, N. Y., A CORPORATION OF NEVYORK r v v i DUPLEX TELEGRAPH s sirnM Application filed October 30, 1828. Serial No. 316,019,.

This invention relates .to a duplex telegraphlc system and in particularto a duplex system providedwith means to reduce or eliminate. the effect of disturbing'currents upon the receiving instrumentsQ An object or this invention is to devise a provision is also made for duplex transmis-Y .sion over the receiving conductor without disturbing the receiving relay. v

The invention is illustrated in the accompanying drawing in which like parts inthe various figures are indicated by the same reference characters.

Figure l is a circuit diagram of the invention;

Figure l illustrates the circuit of Figure 1 arranged in a different manner for the purpose of explaining 1ts operation.

Referring to the drawing, LC indicates a line conductor over which telegraphic messages are to be received and transmitted. llhe line conductor is subject to disturbing currents induced therein by neighboring power circuits and the like.

In Figure 1, a circuit is completed from the line conductor LC through a resistance R through two windings and of a receiving relay, through resistance R and through an artificial line AL to ground. The operating windings and W of the receiving relay are connected inseries, and a tr'ans-. mitter TB is connected at one terminal to a point between the windings and V and at theother terminal to the ground. A tuned path, including inductance coil L and a condenser C in parallel, is connected in shunt to resistance R and windings W and W In a like manner, a tuned path, including inductance coil L and condenser C in parallel, is connected in shunt to windings V and Vi, and resistance R By reference to Figure 1, it will be seen that the resistance R and R and the two tuned paths, constitute, respectively,the arms of a balanced Vheatstone bridge with the receiving relay circuit connected in a diagonal of the bridge.

The operation 1s as follows:

qTli *two tuned arms of the bridge-are adjusted'to'resonance with the disturbing currents, which are usually alternating currents of or'60cycles frequency induced by neighboring power lines. Besistance'R is adjusted in value to equal the resonant impedance of the tuned arm including'coil L 'and con- 'denser.C Also,fresistan'ce R isadjusted in value to equalthe resonant 'impedanceof the tuned'arm' including condenser C and coil'L' Under the foregoing conditions, the bridge will beibalanced with respect to the disturblng currents, and the receiving relay will-not be operated thereby; However, for

incoming telegraphic signals the tuned arms of the bridge w ll n otibe balanced by the resistance arms, and signal currents Wlll flow through windings W? and VV of the relay and effect its operation. Upon transmitting signals from transmitter TR, the transmitted current flows through windings N and in opposite directions and, therefore, the re ceiving relay will not be operated. Artificial line AL is adjusted in impedance to produce a balanced relation between transmitter TR and the receiving relay; In other words, transmitter TR- is in conjugate relation with the receiving relay. 1

Due to the facttha'tthe tuned arms of the bridge include the parallel resonant circuits. the resonant impedances of thesearms will be relatively high, and resistances R and R will be correspondingly high,as compared with the impedance of seriestuned circuits including the same elements.

One of the advantages of the invention is its simplicity and its adaptability to stand ard duplex and multiplex systems already in operation without modification of the telegraph equipment. y

We claim:

1. In a duplex telegraph system, the combination of a line conductor subject to disturbing currents, a return path for said line conductor, an artificial line connected to said return path, a IVheatstone bridge connected between the line and the artificial line and comprising two opposite arms each of which includes a parallel resonant circuit tuned to the disturbing current, and two opposite resistance arms, a receiving relay connected in a diagonal of said bridge, and a transmitting circuit in conjugate relation with said relay, said resistance arms being adjusted in value to equal the resonant impedances of the adjacent arms respectively, and said artificial line having an impedance such as to produce a duplex balance of the system.

2. In a duplex telegraph system, the con1- bination of a line conductor subject to disturbing currents, a return path for said line conductor, an artificial line connected to said return path, a balanced IVheatstone bridge connected between said artificial line and said line conductor, two opposite arms of said bridge eachincluding a parallel resonant circuit tuned to the disturbing current, and the two opposite remainingarms comprising resistance elements equal in value to the re-- sonant impedances of the adjacent tuned arm's respectively, a rece ving relay havlng (two operating wlndings connected in "series in a diagonal of said bridge, and :a transmitting circuit connected between said return .path and appoint between said operating windings, said artificial line being of such value that said system is balanced for duplex operation. 7 V

In testimony whereof we aflix our signatures.

JOSEPH WV, MILNQB, WILLIAM D. CANNON. 

